Nets of synthetic threads



May 22, 1962 l KE ETAL 3,035,475

Mza.

'exposed during their use.

United States Patent Oiiice 3,035,475 Patented May 22, 1962 3,035,475 NETS F SYNTHETHC 'El-READS Heinrich Rnke and Erwin Windemuth, Leverkusen, Germany, assignors, by direct and mesne assignments, of one-half to Farbenfabriken Bayer Aktiengesellschaft, Leverkusen, Germany, a corporation of Germany, and one-half to Mobay Chemical Company, Pittsburgh, Pa., a corporation of Delaware Filed Feb. 19, 1957, Ser. No. 641,022 Claims priority, application Germany Feb. 23, 1956 2 Claims. (Cl. 87.--1)

This invention relates generally to synthetic threads and nets made therefrom and more particularly to synthetic threads having their surface modified to prevent slippage of knots tied therefrom.

It has been proposed heretofore to manufacture nets from threads or yarn made from synthetic fibers, Such nets are particularly desirable because the synthetic liber is substantially unaffected by water and by any salts that may be dissolved in the water. The heretofore available nets made from synthetic fibers have had the disadvantage, however, of having a smooth, slick surface and consequently it has been impossible to tie one thread about another to form a knot which will not slip as the net is being formed or as it is handled when it is used. Slippage of the knot is, of course, undesirable because the mesh and shape of the net is modified. Efforts have -been made to tie the knots so tightly that they cannot slip, but the synthetic threads frequently break under the tension required to tie such a knot. Moreover, the physical properties of the synthetic thread are adversely affected by stretching under such high degrees of tension.

It has also been proposed to surface-coat threads used in tying nets with a resinous material eg. shellac that provides the thread with a surface which will prevent the knots from slipping. In this process the nets are dipped in a suitable solution of the resin and dried at relatively high temperatures. Such a process is very cumbersome particularly with large nets and, moreover, the surface coating Will frequently swell more than the underlying thread when the net is subjected to moisture or Water. Because of the unsuitability of the nets made by coating them after they have been tied, some attempts have been made to coat the threads prior to their use in forming the nets. The heretofore available coatings for the threads have not been suitable, however, because they adversely aect the translucency of the underlying thread or yarn and in many instances the coating swells under the iniluence of moisture or water to a different extent than the thread. Moreover, such coatings vfrequently become cloudy when exposed to moisture and will not withstand the chang to which nets are frequently subjected.

lt is therefore an object of this invention to provide synthetic threads adapted to be tied to each other in nonslip knots. Another object of 4the invention is to provide synthetic threads having improved tying properties. A

.further object of the invention is to provide synthetic threads and yarns particularly Well suited for use in tying knots in forming nets which have a surface coating that prevents slippage of the knots and does not adversely affect the physical characteristics of the thread. Still another object of the invention is to provide nets formed from synthetic fibers which will maintain their shape and mesh under the adverse conditions to which nets are A still further object of the invention is to provide threads for making nets which can be tied into non-slip knots and are flexible and tough and thus have improved strength and elongation characteristics.

The foregoing objects will become more apparent with reference to the accompanying drawing in which FIGURE 1 illustrates a portion of a net in accordance with this invention; and

FIGURE 2 is a cross-sectional view of ya thread taken along lines II--II of FIGURE l.

ln accordance with this invention, generally speaking, the foregoing objects and others which Will become apparent from the following description are accomplished by providing synthetic threads with a surface film of an organic polyisocyanate and an organic compound having a reactive hydrogen atom of high molecular weight adapted to react with the poly-isocyanate to for-m a cross-linked polyurethane resin. It has been found that a surface iilm of plastic material which can be converted into an insoluble cross-linked polyurethane by chemical reaction after it has been yapplied to the thread will provide a surface on synthetic threads which prevents slippage of kno-ts tied therefrom. Ordinarily, the chemical reaction which results in cross-linking is brought about by heating Ithe thread after the coating has been -applied by any other suitable means may be utilized. The surface film may be applied to the thread by a coating or impregnating process. The material the thread is coated or impregnated with penetrates into the outer parts of the thread thereby irmly anchoring the surface film onto lthe thread.

The threads and yarns which have proved to be most advantageous for use in forming nets and similar knotted structures are impregnated with a solution of the polyisocyanate and organic compound having the reactive hydrogen atom. The organic compound having the reactive hydrogen atom may be any suitable polyhydroxy compound of rela-tively high molecular weight, i.e. of more than 400, such as, for example, polyester-s produced by esteriiication of dicarboxylic acids with an excess of a polyhydric alcohol, preferably a glycol, hydroxy carboxylic acids, including citric acid and tri-carballyl acid, polyesteramides having terminal hydroxyl groups obtained by including an amino alcohol, such as, for example, diethanolamine, along with dicarboxylic acid in the condensation with a polyhydric alcohol. Other examples o-f suitable polyhydroxyl compounds include polyalkylene ether glycols and polyalkylene thioether glycols having terminal hydroxyl groups, `and polyesters formed from phthalic acid and glycerol modified with fatty acids.

Those hlm-forming materials which provide the greatest degree of holding power of the knots or, in other words, provide the most advantageous surface to the thread, are formed by blending compositions which would ordinarily form a soft coating with compositions which would ordinarily form a hard coating. Linear polyhydroxy compounds tend to produce a soft coating, whereas, branched polyhydroxy compounds tend to form hard coatings. The most advantageous service is obtained when some quanti-ty of residues of trifunctional starting materials is present in the polyhydroxy compound. Preferably, if maximum non-slip properties are desired a polyhydroxy compound or mixtures thereof should be used which contain not more than 15% of molecular residues of trifunctional starting materials. To comply Vwith this requirement, however, the blending proportions of several polyhydroxy compounds can be varied within wide limits according to the degree of hardness, softness and flexibility which is desired.

Any suitable polyisocyanate may be utilized in preparing the composition used for coating or impregnating the synthetic thread, Representative examples include 1,2,4-toluylene diisocyanate, 1,2,6-toluylene diisocyanate, a mixture of these two diisocyanates, meta-phenylene diisocyanate, dimethyl diphenyl methane-4,4-diisocyanate and the like. The reaction products obtained from a reaction between a dsocyanate and a polyfunctional hydroxyl compound, such as, for example, ethylene glycol, glycerol, trimethylol propane and hexane triol, may also be utilized, but if such a product is to be used, an excess of the isocyanate should be used to insure that the product has terminal -NCO groups. Isocyanate-modied polyhydroxy compounds of relatively high molecular weight having free -NCO groups, such as, for example, isocyanate-modied polyesters having terminal NCO groups, may also be used. The isocyanate used in forming the coating or impregnating composition may also be in the form of a blocked isocyanate or, in other words, the reaction product of hydrocyanic acid, phenol, maleic or aceto-acetic esters with an isocyanate. Such compounds are stable at ordinary temperatures but decompose when the temperature is elevated and revert to the original isocyanate compound.

As will be more apparent from the embodiments described hereinafter, the thread is coated with a solution of the polyester or other polyhydroxy compound and the polyisocyanate, the excess solution is removed from the thread by conventional means, and the remaining coating is heated to remove the solvent and to bring about reaction between the polyhydroxy compound and polyisocyanate to form a polyurethane plastic surface on the thread. The reaction may be accelerated by the use of conventional catalysts, such as tertiary amines and heavy metal salts.

The synthetic threads, which may be treated in accordance with this invention and used for forming nets adapted to retain their shape and mesh under the conditions to which they are exposed while being used, may be formed from any suitable synthetic fiber, but they are preferably formed from a polyamide, a polyurethane, a polyester, or a polyacrylonitiile. The threads may be formed by any conventional extrusion or other process suitable for shaping soft plastic masses into threads or filaments.

The yarn or thread to be used according to the invention is preferably impregnated by passing it through a dipping bath of a mixed solution of the said components. Any suitable volatile organic solvents such as acetic ester, acetone, trichlorethylene, methylene chloride, methyl ethyl ketone, monomethyl glycol ether acetate, benzene, toluene, or tetrahydrofuran, which permit a high speed of preparation due to their rapid evaporation, have proved to be particularly suitable as solvents. In many cases, it has proved to be desirable to accelerate the reaction velocity of the components by adding catalysts, as, for example, tertiary amines such as N,Ndimethyl piperazine or organic metal complex compounds such as iron acetyl acetonate. Basic catalysts can also be directly incorporated as tertiary amines into the polyhydroxy component, for example, by the concurrent use of triethanolamine.

Subsequently to the impregnation, the thread is preferably passed through a reaction chamber which is heated to approximately 200 C. and through which air is simultaneously passed for rapidly removing the solvent. The speed at which the thread or yarn is passed through this heating chamber for the evaporation of the solvent and for carrying out the polyaddition is so adjusted that the thread cannot become heated to a temperature higher than about 11G-120 C. owing to the evaporation of the solvent. Under these conditions, the physical properties of the thread do not undergo any change Working speeds Iup to about 300 m./ min. can be obtained, depending on the length of the heating chamber, the speed and the temperature of the air injected into the latter and the thickness of the thread to be prepared.

The amount of coating to be applied to the thread depends upon the nature of the thread and can easily be determined by preliminary tests. A coating of about 2-4% has proved to be sufficient with multithread yarn, while this coating proportion is preferably between about 4 and 10% with a thin monofllar yarn.

The use of fully synthetic yarns and threads impregnated in this manner for forming knotted structures makes it possible to produce nets which are particularly suitable for fishing purposes, which nets can be produced by knotting without the application of great force and yet are completely non-slipping. Such nets also Cornpletely maintain their dimensions, even when used frequently in sea water under strong tensile stressing.

Example I A polyamide thread or cord made from caprolactam is impregnated in the following impreguating solution:

About l0 grams of a polyester made from about 3 mols of adipic acid, about l mol of trimethylol propane and about 3 mols 0f butylene glycol, about l0 g. of a polyester from about 16 mols of adipic acid, about l mol of trimethylol propane and about 16 mols of diethylene glycol, as well as about 9.2 g. of a reaction product from about 3 mols of toluylene diisocyanate and about l mol of hexanetriol, are dissolved in about 980 g. of acetic ester. After about l0 mg. of iron acetyl acetonate have been added to this solution, the cable consisting of about separate tilaments and with a total denier of about 2,700 is passed through this solution at a speed of about 40 m./min.

So much excess bath liquid is removed by passing the cable over stripper bars that the cable takes up about 10 g./min. of the solution, the weight of the thread after it has been completely dried being increased by about 2.5%. The thread is then passed freely through a vertically disposed tube Which is heated to about C. and which has a length of about 4.6 m. The two ends of the tube are closed except for small passage openings for the thread. Air heated to about 190 C. is injected at a rate of about 40 cubic meters per hour into the bottom end of the tube for more rapidly removing the solvent, which is largely recovered from the waste air (at the upper end of the shaft) by suitable cooling installations. After the `thread has left the heating shaft, air is blown onto the thread for a short time, whereby the thread is cooled, and the thread is then wound with a tension of about 250-300 g.

The physical properties of the thread are not changed by this treatment, The individual threads show no sign of sticking to one another and are highly lustrous. After a number of threads have been twisted together to form a yarn usual in the net-making industry, it is possible to produce nets which can be knotted without the application of great force and yield knots which are completely non-slipping. Such nets are also completely true to shape even after being frequently used in salt water while subject to strong tensile stressing.

Example 2 A polyamide yarn made from caprolactam suitable for the production of knotted structures is also obtained, if, in the impregnating liquid described in Example l, the diisocyanate-hexanetriol reaction product is replaced by about 3.3 g. of m-phenylene diisocyanate. An accelerator is not necessary with this formulation.

Example 3 Using the working conditions of Example 1, a polyamide monolament made from caprolactam with a diameter of about 0.20 mm. is impregnated at a speed of about 50 m./min. with about an 8% solution of the following composition:

About 16 g. of a polyester from about 3 mols of adipic acid, about 3 mols of butylene glycol and about 1 mol of trimethylol propane, about 4 g. of a polyester from about 2 mols of adipic acid, about 0.5 mol of phthalic acid, about 2.5 mols of trimethylol propane and about 1 mol of butylene glycol; about 23 g. of about a 60% acetic ester solution of a reaction product from about 3 mols of dimethyl diphenyl methane-4,4diisocyanate and about 1 mol of trimethylol propane; about 408 yg. of acetic ester; and about 9 mg. of iron acetyl acetonate.

About 50 meters of this thread entrain about 1.2 g. of the above solution in one minute, this corresponding to a coating of about 4.1%. 'I'he knots produced with this thread in the usual manner on a net-knotting machine maintain their position in an excellent manner and cannot be opened by moving the threads relatively to one another.

Example 4 In accordance with the working conditions mentioned in Example 1, a cable made from polyethylene terephthalate, the cable consisting of about 950 separate filaments and with a total denier of about 3000, is passed through a solution of about 10 g. of a polyester formed from about 16 mols of adipic acid, about 16 mols of diethylene glycol and about 1 mol of trimethylol propane, about 10 g. of a polyester from terephthalic acid, glycol, butylene glycol and glycerol and about 17.1 g. of a reaction product from about 3 mols of dimethyl-diphenyl methane-4,4diiso cyanate and about 1 mol of hexanetriol in about 1250 g. of acetic ester.

The reaction of the impregnation is accelerated by adding about 20 mg. of the dicarbamic acid ester from about 2 mols of phenyl isocyanate and methyl diethanolamine.

About 40 meters of the cable take up about 15 g. of the above solution, so that the thread has an application of about 3.8% after the solvent has evaporated. These threads can be knotted easily and securely.

Example 5 In accordance with the working conditions mentioned in Example 1, a polyamide cable (about 2,700 denier) made from caprolactam is passed through a solution of about g. of a branched polythioether formed from about 7 mols of thiodiglycol, about 2 mols of butylene glycol, about 3 mols of bis-hydroxyethyl diphenyl-dimethyl methane and about 4 mols of trimethylol propane with about 1.69% OH, about 7.5 g. of a linear polythioether from about 1 mol of thiodiglycol and about 1 mol of Ibutanediol with about 5.7% OH, and about 19 g. of a reaction product 4from about 3 mols of dimethyldiphenyl methane-4,4diisocyanate and about 1 mol of hexanetriol, in about 1340 g. of acetic ester.

About 3300 meters of the above cable (-:about 1 kg.) take up about 835 g. of the above solution, so that the cable has a coating of about 2.5% after the solvent has evaporated. The threads can be knotted very easily and the knots cannot slip.

Nets are made from the threads produced in the foregoing examples by conventional tying or weaving processes and the knots in the resulting nets do not slip under tension, whereby the nets maintain their shape and size under ordinary handling.

Although the invention has been described in the fore- `going for the purpose of illustration, it is to bey understood that such detail is solely for this purpose and that variations may be made by those skilled in the art without departing from the spirit and scope of the invention except as may be set forth in the claims.

What is claimed is:

l. A net comprising synthetic threads tied together at intervals into knots to form mesh, each of said threads having a coating of from about 2% to about 10% by weight, based on the Weight of the coated thread, of a cross-linked polyurethane plastic rmly anchored thereon, whereby .said knots are non-slipping and said net will maintain its shape and mesh under adverse conditions.

2. A net comprising synthetic threads tied together at intervals into knots to form mesh, each of said threads having a coating of from about 2% to about 10% by weight, based on the Weight of the coated thread, of a cross-linked polyurethane plastic which is the reaction product of a polyisocyanate and a mixture of a dihydroxy compound and a polyhydroxy compound having at least three hydroxyl groups, said mixture containing not more than about 15% polyhydroxy compound having at least three hydroxyl groups.

References Cited in the iile of this patent UNITED STATES PATENTS 2,531,392 Breslow Nov. 28, 1950 2,590,586 Thompson et a1 Mar. 25, 1952 2,676,164 Charlton et al Apr. 20, 1954 2,721,811 Dacey et al Oct. 25, 1955 2,755,266 Brenschede July 17, 1956 2,823,575 Needham et al Feb. 18, 1958 2,862,281 Klausner Dec. 2, 1958 2,866,722 Gensel et al Dec. 30, 1958 2,873,266 Urs IFeb. 10, 1959 2,884,336 Loshaek Apr. 28, 1959 2,929,737 Tishbein Mar. 22, 1960 2,929,794 Simon Mar. 22, 1960 FOREIGN PATENTS 685,623 Great Britain I an. 7, 1953 

1. A NET COMPRISING SYNTHETIC THREADS TIED TOGETHER AT INTERVALS INTO KNOTS TO FORM MESH, EACH OF SAID THREADS HAVING A COATING OF FROM ABOUT 2% TO ABOUT 10% BY 